<html>
<body>
  <script src="common.js"></script>
  <script>
    function checkSubframeImage() {
      return imageLoadedPromise(window.frames[0].document.images[0]);
    }
  </script>
  <img src="image.png?mainframe"/>
  <iframe src="image_delayed_load.html"></iframe>
</body>
</html>